The invention relates to optical imaging and code reading devices. More particularly, the invention relates to a CCD-based imaging apparatus having an imaging engine that is mounted on the hand of the user. A preferred embodiment is a ring imager with a separate decoding unit in communication with the ring imager.
Imaging devices are frequently used for identifying or extracting data from optical codes and are sometimes referred to as xe2x80x9coptical code readersxe2x80x9d, of which barcode scanners are one type. Optical code readers are used in both fixed and portable installations in many diverse environments such as in stores for check-out services, in manufacturing locations for work flow and inventory control and in transport vehicles for tracking package handling. The optical code can be used as a rapid, generalized means of data entry, for example, by reading a target barcode from a printed listing of many barcodes. In some uses, the optical code reader is connected to a portable data processing device or a data collection and transmission device. The optical code reader usually includes a scanner which is manually directed at a target code.
Most conventional optical scanning systems are designed to read one-dimensional barcode symbols. The barcode is a pattern of variable-width rectangular bars separated by fixed or variable width spaces. The bars and spaces have different light reflecting characteristics. One example of a one dimensional barcode is the UPC/EAN code used to identify, for example, product inventory. An example of a two-dimensional or stacked barcode is the PDF417 barcode. A description of PDF417 barcode and techniques for decoding it are disclosed in U.S. Pat. No. 5,635,697 to Shellhammer et al., and assigned to Symbol Technologies, Inc., which is incorporated herein by reference. Another conventional optical code is known as xe2x80x9cMaxiCodexe2x80x9d. It consists of a central finder pattern or bull""s eye center and a grid of hexagons surrounding the central finder. It should be noted that the aspects of the inventions disclosed in this patent application are applicable to optical code readers, in general, without regard to the particular type of optical codes which they are adapted to read. The invention described may also be applicable to some associated image recognition or analysis.
Many scanners in use today employ a scanning laser beam. One example of such a system is disclosed in U.S. Pat. No. 5,543,610 to Bard et al. and assigned to Symbol Technologies Inc., the disclosure of which is incorporated herein by reference. The bar code scanning arrangement described therein includes a scanning unit having first housing adapted to be worn on a user""s finger. The first housing contains a device for generating and directing a scanning laser beam onto a target. The scanning light beam is reflected off the target and received by the scanning unit. An electrical signal is generated in response to the reflected light, which is then sent to a signal processor contained within a second housing. Such an arrangement advantageously affords the operator use of both hands.
In another form of scanning device, it is known in the art to use an image sensor which has a two dimensional array of photo sensors. One such sensor comprises a charge coupled device (CCD) photo detector and objective lens assembly disposed in an optical code reader. One example of such an arrangement can be found in U.S. Pat. No. 5,550,366 to Roustaei. The device disclosed therein includes focusing and receiving optics, a CCD detector array mounted to a printed circuit board, a storage buffer, and a decoder, all contained within the same housing which is adapted to be worn on the back of a user""s hand.
It is an object of the present invention to provide an imaging device including an imaging scanner unit which is sufficiently compact such that it can be contained within a housing adapted to be worn on the user""s finger, and a second separate decoder unit which may be worn about the user""s wrist.
The present invention relates to methods and apparatus useful in imaging, for example, in optical code readers. Techniques are disclosed which are applicable to the design of imaging engines, imaging lens systems, illumination, and signal processing devices associated with code readers of various types.
An optical scanning unit or imager constructed according to the principles of the present invention may comprise an image sensor, an objective lens having an optical axis for directing an image of a target onto the image sensor, at least one circuit board carrying circuitry connected to the image sensor for providing electronic signals corresponding to information for a target image, a reflective element incident to the optical axis for reflecting the target image onto the image sensor, and wherein the image sensor is arranged such that it is not incident to the optical axis. The optical scanning unit is sufficiently compact such that it can be easily worn on the fingers of the user, preferably on a single finger of the user. Alternatively, the optical scanning unit may be worn on the back of the user""s hand.
The housing of the optical scanning unit may contain an illumination apparatus, lens assembly, image sensor and support circuitry. Optionally, an aiming system may also be incorporated into the optical reading unit.
An imaging apparatus constructed according to a further embodiment of the present invention comprises an optical scanning unit and a decoder unit.
According to the present invention, the decoder unit can comprise a housing that can be made sufficiently compact such that it can be worn on the wrist of the user. The decoder unit housing contains a receiver/amplifier, analog/digital converter, FPGA circuitry, power supply and associated power supply control, microprocessor and associated memory devices. Optionally, a device for transmitting information to a remote apparatus, such as a serial port and/or a radio transmitter may also be incorporated into the decoder unit.
An imaging apparatus for the optical code reader may be based on a solid-state image sensor, including an array of photo sensor cells for producing electronic signals corresponding to a two-dimensional array of pixel information for a field of view. Such image sensors include CCD, CMOS, CMD, or CID devices. In preferred embodiments, the image sensor is a CCD. A compact lens assembly is provided for focusing light onto the image sensor.
In certain embodiments, the imaging unit housing is less that two cubic inches in volume, for example, approximately 1.61 cubic inches in volume or less, and is dimensioned to replace a moving laser beam scanning engine in conventional ring scanner units. Such an imaging scanner may be designed to read a variety of types of optical codes.
The imaging systems of the present invention may further include frame grabbing circuitry for providing video signals for displaying images produced by the apparatus on a terminal monitor. In this case hardware modification of existing terminals may be avoided.
In preferred embodiments of the present invention the lens assembly includes compound lenses made up of multiple lens elements aligned on the same optical axis. In other preferred embodiments, the lenses have apertures less than {fraction (1/10)} inch in diameter. The lenses themselves may include inexpensive molded plastic spherical lens elements. Each lens may include two concave-convex lenses with spherical convex surfaces and diameters less than xc2xd inch. The lens elements may be snap fit in an alignment tube or barrel to maintain the lenses in position on a common optical axis in back-to-back relationship.
Imaging unit embodiments of the present invention may also include a target illumination source which emits light from a forward face of the engine. The illumination source may comprise plural light emitting diodes, each associated with a focusing lenslet located in a front face of the reader. The illumination source may have two or more illumination fields or beams. In an illumination system using plural light emitting elements, certain intensity variations may occur across the illuminated field. In preferred embodiments of the present invention, image processing circuits and/or software compensates signals from the image sensor for known variations in illumination provided by the illumination source.
Aspects of imaging engine design are as described in detail in commonly assigned U.S. patent application Ser. No. 09/096,578, the disclosure of which is incorporated herein by reference.
Preferred embodiments may include circuitry and/or software for processing and decoding image data received from the image sensor. An image sensor produces electronic signals corresponding to a two-dimensional array of pixel information for a target image. This data is analyzed by circuitry/software based systems to determine black and white threshold information. The pixel data is divided into subimages, for example, 32xc3x9732 pixel subimages. These subimages are analyzed for properties known to be associated with various types of optical codes and known to distinguish a particular code from other codes and from environmental (non-code) images. In preferred embodiments, the ring imager is capable of reading one dimensional and two dimensional bar codes, postal codes and/or Maxi codes.
In preferred embodiments, an auto-discrimination system determines which subimages contain codes of a particular type and the coordinates in the pixel data array of certain boundaries or features of preliminarily identified code areas. Further circuitry and/or software extracts one or more waveforms from the data in image areas of interest. Peaks and valleys in the waveforms are identified. A digitizer converts this information to electronic signals corresponding to the code content of the image. The output of the digitizer is applied to a decoder which provides a decoded data output or indicates a failure to decode, which may then trigger additional auto-discrimination in a further attempt to identify and locate a decodable image.
Methods and systems for digitization, auto-discrimination and line drawing are disclosed in detail in commonly assigned U.S. patent application Ser. Nos. 09/096,348 and 09/096,164, the disclosures of which are incorporated herein by reference.
The scope of the present invention is as defined in the claims.